Updates Travis config to test against PHP 7.1 and 7.2
Updates Travis config to test against PHP 7.1 and 7.2

Updates the travis configuration to add jobs for PHP 7.1 and 7.2.
Additionally, it removes documentation build directives, as those are
now handled via a webhook.

Finally, it also updates how code coverage is installed and uploaded.

zendframework/zend-xmlrpc